HELP...930 front caliper...pulling again!

[NY65912]

Hi guys, I just finished rebuilding my front calipers (930). Car had been pulling to right only under very hard braking. Sooo I rebuilt the right caliper, easy, no obvious problems with the caliper.

Reinstalled everthing, bled brakes and still same problems!
Install new ss lines.
Tire pressures equal. No leaks, it looked like a sucess but noooo!

Regular braking, no problem. I cleaned the caliper real well and greased the contact points of the pads on the guides with caliper grease, you know, I really tried to be carefull and do it right.

This is not the first time I have rebuilt calipers, I can't figure this one out.

I did a search both before and after the job and found a lot of good info but now I must reach out and ask for help.

PS: Don't forget to block off the MC reservoir if your using a power bleeder so that fluid does'nt pour out of the overflow when you pressurize the system! Ask me how I know.

Thanks.................Mike

[Trust Me]

Went down the same road with the Power Bleeder. Sorry to hear it. Great item though. When you installed the new lines. Did you check to make sure there was nothing in them? Sounds stupid, ya never know. Did you rub the pistons down with steel wool? Not the ruff stuff. 0000.

[dickster]

if its pulling right wouldnt the problem be with the left hand side (not working as well as the right)? just a thought.

i would probably overall both at the same time.

[NY65912]

Dickster..........I thought that would be the case, I have pulled the caliper off again and two of the pistons were "stuck" in the bores and I had to apply a lot more air pressure to pop them out. One piston on each side were standing taller than it's mate.

I really do not want to buy new calipers because everything looks so good on the existing one. The pistons look great. I just took some 2000 paper and rubbed down the pistons on a flat surface, looks a though there might have been some high spots.

It takes a lot of force to put the pistons back into the bores past the seals.........sound right???

I'll keep at it.

Thanks, Mike

[Trust Me]

No. It does not take a lot of force to put the pistons back in. I would not recomend sand paper on the pistons. 0000 steel wool just to "polish" them a bit. Did you lube the seal and the piston before you put them together?

[RoninLB]

Hey Mike

http://forums.pelicanparts.com/showthread.php?threadid=178759

[NY65912]

Ron....thanks but I think I see the problem. OK, I removed the caliper in question and two of the pistons were very slow to come out under pressure. I flattened the sides of the pistons as described in my 1st reply, I polished the pistons using 0000 steel wool and greased everything up again.

Put everything back together, the pistons went in easier and the disc now rotates MUCH more free! One of the pistons must have been hanging up or something. The right side IS better.

As per Dickster's advice I checked the left side.....AH HA!!!

It all came back to me! A few weeks ago when this thing started I was backing the car out of the garage and the brakes were "locked" and then popped free.

So, I took off the left caliper to find it uglier than the right. When I removed the pads the thin plate that is part of the pad came off the pad upon removal. The pistons look in worse shape than the other side. I believe that the left caliper was not doing it's job and the right took all of the load of braking.

I shall do the surgery tomorrow and let you all know how the patient is doing.

Thanks again, Mike

[RoninLB]

Originally posted by NY65912

Ron....thanks but I think I see the problem.

cool

[Trust Me]

Let us know how it goes.

[NY65912]

Well. I did the left side caliper rebuild today. I worked like a surgeon. Polished the pistons, blew everything out multiple time with brake clean and compressed air....real clean. Everything nice.

Changed to SS lines. Fresh fluid. Pads looked good and meaty.

Took it out for a test drive. First few stops at normal speeds were fine, nice and straight. Did a few hard braking stops and started pulling to the right.

Did a few high speed braking 55-60 mph and the front right caliper locked up and pulled to the right.

Did it again and both calipers locked up and the car was rather straight.

Did another run and the left front caliper locked up and pulled to the left.

Now she pulls to the left under normal ( a little hard) braking no longer the right!

OK......do I give up and give Wayne more of my retirement money for new 930 calipers? Do I try new pads? The rotors look fine.

Everything went by the book on the rebuilding of the calipers.....maybe break in period?

HELP!!

Regards,
Mike

[Fast951]

Swap the front tire L to R.. Perform the same braking test as above. If one of your tires has a flat spot, it makes braking very interesting.

I had a similar problem on my 930, replaced the calipers, but problem did not go away. Swapped tires and the car behaved totally different...

[NY65912]

I'm going to use the car for a few weeks with new Mintex pads and see how things go. I will be very cautious and not go above a safe speed.

Any thoughts?


Mike

[RoninLB]

Originally posted by NY65912

I'm going to use the car for a few weeks with new Mintex pads and see how things go.

is it possible that the pads wern't heated when you locked them up?

I kinda had the same prob with stock pads and changed to a soft pad that's great on the street. And I know exactly when they'll fade. I tested them going downhill in the mts.

[88 Club Sport]

Similar thing happend to me this weekend. I ran one day at the track....all ok. On the way home from the track, it pulled to the right when braking hard.

I pulled the wheels found the out board piston on the passenger side was not even close to hitting the pad (at least a 1/4 inch away). Clearly it was stuck in the bore. While applying pressure to the peddle, I had a another person hit the caliper with a rubber hammer...it popped out.

I ran all day Sunday at the track and all was on but the same thing hapended on the way home.

I understand that the piston can get stuck in the bore but what could possibly cause it to back out a 1/4 inch like it is doing?

[NY65912]

Problem fixed! I rebuilt both calipers (to be on the safe side & ss braske lines), and car still pulled to the right then left.

I just came back from my tire guy, who is my next door neighbor and we put on a new set of Dunlop Sport 8000's

WOW, what a difference, I thought the car handled great before....now it handles like it's on rails, and no more pulling!

Thanks for the input